Last year I was able to switch tasksel to using metapackages, instead of the weird non-package task things that had been used before Debian supported Recommends fields well.
An unanticipated result of the new task packages is that I have this nice popcon data available for them, so can get graphs like these.
For new installs of testing, KDE and Xfce are neck and neck. With Gnome being the default, it's hard to say which desktop users really prefer. My feeling is that it's probably nearly evenly split now.
(I installed Xfce on my sister's laptop last week, and anticipate moving all my family to it, rather than Gnome 3.)
The above graph also shows a surprisingly large number of ssh server task installs. In fact, it's the most often manually installed task. Probably many of those are server machines, and so I'm considering having tasksel automatically select ssh on systems where it doesn't automatically select a desktop.
Language data is also available. Taskel uses language tasks internally, without exposing an interface, so this will be almost entirely users who did an install of testing localised to their language.
Interesting data can be teased out of this too. For example there seem more installs in Catalan than Chinese ... and at least 10 Esperanto users. (As with any popcon number, this is a lower bound, to be multiplied by the scaling guesstimate of your choice.)
By the way, I've got a new vanity domain for my blog and wiki: http://joeyh.name/